DAKAR: The World Health Organization has declared an end to the yellow fever outbreak that killed about 400 people in Congo and Angola, calling it "one of the largest and most challenging" in recent years.

The outbreak, first detected in Angola in late 2015, caused 965 confirmed cases and thousands of suspected cases in both countries, the WHO said in a statement Tuesday. Neither country has reported a new confirmed case in the past six months.

Angola in late December declared an end to its outbreak, and Congo made its announcement Tuesday.

The global health agency said more than 30 million people were vaccinated in emergency campaigns to control the outbreak in the two neighboring countries, which have among the world's weakest health systems.

"This unprecedented response exhausted the global stockpile of yellow fever vaccines several times," the WHO statement said.

Regional Emergency Director Dr. Ibrahima Soce Fall warned such outbreaks could become more frequent unless coordinated responses are taken "to vaccinate the population at risk across the region."

There is no known cure for the mosquito-spread virus, which is easily prevented with vaccines. Once infected, people often fall ill with fever and muscle pain, but many recover after several days. The more toxic phase includes possible bleeding from the eyes, ears and nose, jaundice and organ failure